Fluorescence Immunoassay for HBsAg Using a Thermal Phase Separating Polymer

A novel fluorescence immunoassay for HBsAg was developed by using poly-N-isopropylacrylamide (PNIP) as an immunoreaction carrier. In sandwich immunoassay, after two steps immunoreaction, PNIP precipitates out of water above a critical temperature of 31°C, enabling a polymer-bound immune complex to be separated from the solution. The calibration graph for HBsAg was linear over the range of 0.5-100 μg/mL with a detection limit of 10 ng/mL. This method combines some advantages of both homogeneous and heterogeneous immunoassays, and has been applied to determining the HBsAg in human blood serum with satisfactory results.